JP2014-40856A discloses a crankshaft for straight-for engine. This crankshaft includes two flanges, five crank journals, four crank pins and eight crank arms connecting the crank journals and the crank pins. One of the flanges is fitted with a flywheel. In this crankshaft, width and thickness of each crank arm are designed so that stiffness of the crank arm (i.e., bending stiffness and torsional stiffness) increases as a distance from the crank arm to an attachment part of the flywheel decreases.
According to the crankshaft described above, it is possible to reduce noise and vibration of the engine by suppressing wobbling deformation of the flywheel. However, in a V6 engine, there is a vibration mode in which the whole crankshaft is deformed. Therefore, it is not sufficient for noise and vibration of the V6 engine only by suppressing the wobbling deformation of the flywheel.
The present disclosure addresses the problem described above, and an object of the present disclosure is, to provide a crankshaft for V6 engine capable of reducing the noise and vibration of the V6 engine.